The invention relates to the determination of channel quality in communication systems, and more particularly to a determination of a channel quality indicator in a radio communications network.
As the popularity of communication in radio communications networks continues to grow, there has been increased interest in providing packet data communications in radio communications networks. High-Speed Downlink Packet Access (HSDPA) is a service which is currently being developed for providing packet data communications in radio communications networks.
Due to the differences between voice communications and packet data communications, the design of these systems can be quite different. For example, since voice communications in radio communications networks are treated as a single stream of information, a single channel is typically reserved for each voice communication. In contrast, packet data communications can be discontinuous, and hence, many packet data communications can share access to a single channel.
Accordingly, the HSDPA service provides for adaptive modulation in the downlink, i.e., the channel from the communication network to a radio receiver. Specifically, the transport format, (i.e., the channel coding and modulation), that is to be used for transmission by the radio communications network is determined for each transmitted packet. The choice of transport format selected by the radio communications network is based upon a Channel Quality Indicator (CQI) value reported by a radio receiver. The transport format may also be based on the received power control commands or on other information that can be estimated by the base station, e.g., power and quality of the data symbols on the uplink.
The determination of the CQI is based on two components. The first component is likely to be based on a signal-to-interference ratio (SIR) measurement of a pilot channel. The second component of the CQI determination requires that the determined CQI result in a transport block error probability which is approximately 10 percent, without exceeding 10 percent. Therefore, it would be desirable to provide methods and apparatus for determining a particular CQI value which will result in a transport block error probability which is approximately 10 percent, without exceeding 10 percent.